Emergency alarm receiver



Jan. 25, 1966 J, E, ALT ETAL 3,231,881

EMERGENCY ALARM RECEIVER Filed June 6, 1961 United States Patent O 3,231,881 EMERGENCY ALARM RECEIVER John E. Alt and Sydney C. Gearing, Flint, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed June 6, 1961, Ser. No. 115,211 7 Claims. (Cl. 340-310) This invention relates to an emergency alarm receiver, and more particularly, to a time delay circuit for an emergency alarm receiver.

It has been proposed to utilize an air raid warning system whereby upon receipt of an air raid warning, electric power vgenerating stations would superimpose a predetermined signal upon the ordinary power line voltage so that every home serviced by that power generating source would receive an electrical signal. This invention relates to means responsive to such electrical signal to produce an alarm so that each home equipped with such an alarm means would receive warning of the impending air raid.

In particular, it has been proposed that a suitable alarm receiver would be a device which is continually connected to a conventional Wall receptacle and which is responsive to a 24U-cycle signal superimposed upon the conventional 60-cycle line voltage. It has further been proposed to equip the receiver with a time delay of, say, ten seconds so that the 24U-cycle signal would have to be maintained for a period of more than ten seconds in order to actuate the alarm thereby preventing unintentional alarms due to transients in the power lines.

Further, it is contemplated that after the initial time delay, the alarm should render an audible and/or visual warning for a certain period such as fty seconds whereupon the alarm would be discontinued and the receiver to reset to stand-by operation so that subsequent alarms may be given in like manner to the rst alarm.

It is the purpose of this invention to provide an alarm receiver having time delay circuitry for providing the functions described above.

The invention is carried out by providing a time delay circuit including an inductor and means responsive to the temperature of the inductor core to control the operation of the circuit.

Another aspect of the invention is carried out by providing a circuit with an inductor, a vibrating reed associated therewith responsive to a predetermined signal, means associated with said control for producing an alarm after actuation of said vibrating reed, and means responsive to the temperature of said inductor to further control the operation of the alarm means.

The above and other advantages of the invention will be made more apparent from the following specication, taken in conjunction with the accompanying drawings wherein:

FIGURE l is a schematic diagram of a receiver alarm circuit according to the invention;

FIGURE 2 is a front elevational view of an inductor and its associated accessories according to the invention; and

FIGURE 3 is a side elevational view of the inductor of FIGURE 2.

Referring now to FIGURE l, the circuit includes a terminal member suitable for connecting to a conventional household receptacle and has one terminal connected to a line 12 and the other terminal connected to a line 14. A neon lamp 16 in series with a resistor 18 is connected between lines 12 and 14. Also, a resonant circuit comprising an iron core inductor 20 in series with a capacitor 22 is also connected between lines 12 and 14. The resonant circuit is tuned to 240 cycles. Appropriate values of the circuit elements are 0.5 microfarad for the capacitor 22 and 0.88 henry for the inductor 20. The iron core 21 of the inductor 20 has a gap 23, best shown in FIGURE 3, containing a reed 24 tuned to 240 cycles. A stationary contact 25 is provided adjacent the reed to make intermittent connection with the reed 24 upon vibration thereof. The reed 24 in turn is connected in series with one terminal of an A.C. relay 26, the other terminal of which is connected to line 12. A switch 28 operated by the A.C. relay 26 has a stationary contact 34B connected to line 14 and a movable Contact 32 connected to one terminal 34 of an A.C. dashpot-type time delay relay 36. The other terminal 38 of relay 36 is connected to line 12. The time delay relay 36 is operable to close a pair of normally open switches 40 and 42, the

stationary contacts 44 and 46 of which are connected to terminals 34 and 38, respectively, of the relay 36. The movable contact 48 of switch 4t) is connected through a normally close-d bimetal thermal time delay Vswitch 50 which in turn is connected to line 14. The movable contact 52 of switch 42 is connected through a small resistor 53 of, say, about ten ohms to a point between the inductor 2t) and capacitor 22. A 1Z0-cycle clapper S4 is associated with the inductor 20, as best shown in FIG- URE 3, and the thermal time delay switch 50 is also associated with the inductor 2t) in order to sense the temperature thereof.

Referring to FIGURES 2 and 3, the inductor 20 is a coil having a two piece core 21, 21. Each core piece 21, 21 has an F-shaped cross section and has an arm 60 extending into the coil to abut the corresponding arm of the other piece. The remaining arms 62 of the core pieces are shorter than the arms 60, so that an air gap is formed between them. The vibrating reed 24 is located in this gap and has a hexagonal nut 64 on the free end thereof for tuning purposes. A second larger air gap is formed by the ends 66 of the core pieces 21, 21. A 120- cycle clapper 54 is secured to the cover 68 of the receiver and is disposed across the pole piece ends 66 and spaced therefrom so that it will be caused to vibrate by the 60- cycle flux across the air gap. Upon vibration the clapper will rap on the cover 68 to render an alarm. The bimetal switch 5t! is mounted on the side of the core 60 so as to be exposed to the heat generated by the 60-cycle energization of the inductor thereby providing an automatic time delay which depends upon the period of time which a large voltage is applied to the inductor, the thermal relationship of the bimetal portion 51 with the inductor 20 and the characteristics of the bimetal portion 51.

In operation, when the terminal 10 of the receiver is connected to the wall receptacle, lines 12 and 14 will be energized thereby causing the neon lamp 16 to glow to serve as an indication that the receiver is properly connected to the power line and is receiving current. When a conventional 11G-volt 60-cycle voltage is applied across lines 12 and 14, only about eight volts will appear across the inductor 20. The resulting magnetic flux density is insuicient to cause vibration of the 24U-cycle high Q resonant reed 24 which operates in an air gap 23 in the inductor core 21, and also is insufficient to cause operation of the clapper 54. In this standby condition, the

resonant circuit consumes only approximately 23 ma. current.

When a 24U-cycle signal ranging from 0.9 to 6 volts in amplitude is superimposed on the 60-cycle line voltage, maximum 24U-cycle current is passed through the resonant circuit and a maximum 24U-cycle magnetic liuX is provided in the air gap 23 of the inductor 2t). This flux causes the tuned reed 24 to vibrate and intermittently make contact with the stationary contact 25 thereby connecting the A.C. relay 26 to line 14. The energization of the relay 26 causes the switch 28 to close and connect the time delay relay 36 to line 14. The time delay relay is preferably set for ten seconds delay. Assuming that the 24U-cycle signal has been maintained for more than 10 seconds, the' switches .40 and 42 will be closed. Switch 4t) then obviously acts as a holding switch and will maintain the time delay relay 36 energized as long a-s current is supplied to the switch 40 through the thermal switch 50 and is independent of the continuation of the 24()- cycle signal. The closing of `switch 42 serves to shunt out the capacitor 22 so that nearly all of the normal line voltage is applied across the inductor 2t). The small resistor S3 between the switch 42 and the resonant circuit serves as a current limiting device for protecting the :switch contacts 46 and 52 against arcing when capacitor 22 is discharged. The increased 60-eycle flux bridging the open end of the inductor core causes operation of the clapper 54 which bridges the gap. The clapper then raps on the cover of the alarm to produce the desired audible alarm. The normal operational heat rise of the inductor 20 will cause the bimetallic thermal switch 50 to open when the opening temperature of the switch is reached. Preferably, the time-temperature characteristics of the inductor 20 and switch 50 are such that iifty seconds of normal opeartion are required to cause opening of the switch 54) thereby establishing the alarm time at fifty seconds. It is readily seen that the opening of the switch 50 causes deenergization of time delay relay 36 to return the receiver to standby operation after a short cooling period to allow the thermal switch Sti to return to its closed position.

It is apparent, then, that the herein described invention provides a simple and reliable emergency alarm receiver, and further provides a unique time delay circuit which uses standard and inexpensive components and is particularly well adapted to use in an alarm receiver of the type described.

The above described embodiments of the invention are intended only as specific illustrations of the invention and are not to be taken as limiting the scope of the invention which is dened by the following claims:

We claim:

1. In an alarm responsive to a high frequency signal, means for connecting the said alarm to line voltage, an inductor having a magnetic core, signal responsive means magnetically coupled with said core, time delay means energized by said signal responsive means, alarm means energized by said time delay means, and a thermal time delay means in thermally conductive relation to the inductor core and sensitive to the temperature of the inductor core for deenergizing the alarm.

2. In an alarm responsive to a high frequency signal, means for connecting the said alarm to line voltage, an inductor having a magnetic core, signal responsive means magnetically coupled with said core, a time delay circuit energized by said signal responsive means, means responsive to said time delay circuit to impose line voltage on said inductor, alarm means actuated by the magnetic iield arising from the line voltage acting on the inductor, and a thermal time delay means in thermally conductive relation to the inductor core and sensitive to the temperature of the inductor core for deenergizing the alarm.

3. In an alarm responsive to a high frequency signal, means for connecting the said alarm to line voltage, an inductor having a magnetic core, a vibrating reed in said core responsive to said signal, a time delay circuit energized by said reed, means responsive to said time delay circuit to impose line voltage on said inductor, clapper means actuated by the magnetic lield arising from the line voltage acting on the inductor, and a thermal time delay means in thermally conductive relation to the inductor core and sensitive to the temperature of the inductor core for deenergizing the alarm.

4. An alarm comprising means for connection to a power line, a high frequency resonant circuit connected to said means, :said resonant circuit including a capacitor and an inductor in series, a gapped core in said inductor, a tuned reed in the gap of said core responsive to a high frequency signal imposed on said line, means for energizing a relay upon vibration of said reed, means responsive to said relay for energizing a time delay circuit, a rst means actuable by said time delay circuit for shunting out said capacitor whereby substantially the full line voltage will act upon the inductor, a clapper associated with said inductor and responsive to the line voltage energization thereof, a second means actuable by :said time delay circuit for connecting a thermal switch in series with said time delay circuit, said thermal switch being in thermally conductive relation to said core and sensitive to the temperature rise thereof to deenergize said time delay circuit after a predetermined period of line voltage energization of said inductor.

5. An alarm comprising means for connection to a 60- cycle power line, a signal frequency resonant circuit connected to said means, said resonant circuit including a capacitor and an inductor in series, a gapped core in said inductor, a tuned reed in the gap of said core responsive to a signal imposed on said line, means for energizing a relay upon vibration of -said reed, means responsive to said relay to energize a time delay relay, a iirst means actuable by said time delay relay for shunting out said capacitor whereby substantially the full 60-cycle voltage will act upon the inductor, an alarm means associated with said inductor and responsive to the 60-cycle energization thereof, a second means actuable by said time `delay relay for connecting a thermal switch in series with said time delay relay, said thermal switch being physically attached to said core and responsive to the temperature of said core to deenergize said time delay relay after a predetermined period of 60-cycle energization of said inductor.

6. An alarm comprising means for connection to a 6()- cycle power line, a 24U-cycle resonant circuit connected to said means, said resonant circuit including a capacitor and an inductor in series, a gapped core in said inductor, a 24U-cycle tuned reed in the gap of said core responsive to a 24U-cycle signal imposed on said line, means for energizing an A.C. relay upon vibration of said reed, means responsive to said relay to energize a time delay relay, a first means actuable by said time delay relay for shunting out said capacitor whereby substantially the full 60-cycle voltage will act upon the inductor, a clapper associated with said inductor and responsive to the 60-cycle energization thereof, a second means actuable by said time delay relay for connecting a thermal switch in .series with said time delay relay, said thermal switch being physically attached to said core and responsive to the temperature rise of said core to deenergize said time delay relay after a predetermined period of 60-cyc1e energization of said inductor.

7. A time delay circuit comprising an inductor having a magnetic core and a winding, a thermal responsive time delay :switch physically attached to said core in thermally conductive relation therewith and responsive to the temperature of said core, circuit means connecting said switch with said winding, said switch having a predetermined time delay, whereby said switch is operative to deenergize the winding of the inductor a predetermined time after said inductor is energized.

References Cited by the Examiner UNITED STATES PATENTS Miller 200-122 Burnham ZOO-88.2 Deal 340-310 Pearce 20G-88.2 Welch 340-384 X Church 20G-88.2 X

Sprague S40-384 CoIWeIl et a1. 340--310 6 12/1959 Stewart 340-310 2/ 1960 Dawkins et a1. 340--377 7/1961 De Feo 340-216 2/1962 Weber 340--310 X 5/ 1962 Inderwiesen 340-310 X FOREIGN PATENTS 1/1930 France. 9/ 1936 Great Britain. 6/ 1939 Great Britain.

NEIL C. READ, Primary Examinez'.

ELI J. SAX, ROBERT H. ROSE, Examiners. 

1. IN AN ALARM RESPONSIVE TO A HIGH FREQUENCY SIGNAL, MEANS FOR CONNECTING THE SAID ALARM TO LINE VOLTAGE, AN INDUCTOR HAVING A MAGNETIC CORE, SIGNAL RESPONSIVE MEANS MAGNETICALLY COUPLED WITH SAID CORE, TIME DELAY MEANS ENERGIZED BY SAID SIGNAL RESPONSIVE MEANS, ALARM MEANS ENERGIZED BY SAID TIME DELAY MEANS, AND A THERMAL TIME DELAY MEANS IN THERMALLY CONDUCTIVE RELATION TO THE INDUCTOR CORE AND SENSITIVE TO THE TEMPERATURE OF THE INDUCTOR CORE FOR DEENERGIZING THE ALARM.
 7. A TIME DELAY CIRCUIT COMPRISING AN INDUCTOR HAVING A MAGNETIC CORE AND A WINDING, A THERMAL RESPONSIVE TIME DELAY SWITCH PHYSICALLY ATTACHED TO SAID ONE IN THERMALLY CONDUCTIVE RELATION THEREWITH AND RESPONSIVE TO THE TEMPERATURE OF SAID CORE, CIRCUIT MEANS CONNECTING SAID SWITCH WITH SAID WINDING, SAID SWITCH HAVING A PREDETERMINED TIME DELAY, WHEREBY SAID SWITCH IS OPERATIVE TO DEENERGIZE THE WINDING OF THE INDUCTOR A PREDETERMINED TIME AFTER SAID INDUCTOR IS ENERGIZED. 